The human spine contains a series of bony segments separated by discs and coupled together with muscle, ligaments, and other connective tissues. A large number of ailments may afflict one or more of these components. One exemplary ailment generally occurs with age as the spinal discs begin to break down, or degenerate resulting in the loss of fluid in the discs, and consequently, the discs become less flexible. Likewise, the discs become thinner allowing the vertebrae to move closer together. Degeneration also may result in tears or cracks in the outer layer, or annulus, of the disc. Degeneration of the annulus may allow the disc to begin to bulge outwardly. In more severe cases, the inner material of the disc, or nucleus, may extrude out of the disc. In addition to degenerative changes in the disc, the spine may undergo changes due to trauma from automobile accidents, falls, lifting, and other activities. Furthermore, in a process known as spinal stenosis, the spinal canal narrows due to excessive bone growth, thickening of tissue in the canal (such as ligament), or both. In all of these conditions, the spaces through which the spinal cord and the spinal nerve roots pass may become narrowed leading to pressure on the nerve tissue which can cause pain, numbness, weakness, or even paralysis in various parts of the body. Finally, the facet joints between adjacent vertebrae may degenerate and cause localized and/or radiating pain. All of the above conditions, as well as others not specifically mentioned, are collectively referred to herein as spine disease.
Conventionally, surgeons treat spine disease by attempting to restore the normal spacing between adjacent vertebrae. This may be sufficient to relieve pressure from affected nerve tissue. However, it is often necessary to surgically remove disc material, bone, or other tissues that impinge on the nerve tissue and/or to debride the facet joints. Most often, the restoration of vertebral spacing is accomplished by inserting a rigid spacer made of bone, metal, or plastic into the disc space between the adjacent vertebrae and allowing the vertebrae to grow together, or fuse, into a single piece of bone. The vertebrae are typically stabilized during this fusion process with the use of bone plates and/or pedicle screws fastened to the adjacent vertebrae.
Although techniques for placing intervertebral spacers, plates, and pedicle screw fixation systems have become less invasive in recent years, they still require the placement of hardware deep within the surgical site adjacent to the spine. The hardware is frequently related to the intervertebral spacer, itself, along with additional hardware to immobilize the vertebral segment associated with the fusion. The additional hardware also inhibits the spacer from exiting the space. Recovery from such surgery can require several days of hospitalization and long, slow rehabilitation to normal activity levels.
Thus, it would be desirable to provide an implantable intervertebral spacer that presented as low a profile as possible while still providing sufficient hardware to facilitate immobilizing the vertebral segment being fused.